Textile silica sliver, its manufacture and use

ABSTRACT

The textile silica sliver is produced by a continuous process of the dry spinning of sodium silicate filament yarn, direct formation of sodium silicate silver by the drum drawing process, transformation to textile silica sliver in a post-treatment line, and direct winding on of the sliver. The various textile products manufactured from textile silica slivers or staple fiber yarns made therefrom are suitable for application in insulation and heat protection up to 1100° C., substitute for asbestos and improve energy efficiency.

FIELD OF THE INVENTION

The invention relates to textile silica sliver, its manufacture, as wellas the use of the silica sliver.

BACKGROUND OFF THE INVENTION

Textile products made from textile quartz, leached silica and silicafibers have been known in some cases for a long time. They are madeaccording to different processes and consist of pure or nearly puresilicon dioxide (Ullmanns Enzyklopadie der technischen Chemie, 4thEdition (1977) Vol. II, pp. 359-374 , Verlag Chemie, Weinheim/Bergstr.and Melliand Textilber. (1989), pp. 629-632).

Depending on processing conditions and on the single fiber length, thefollowing primary fiber types can be distinguished according to Koch P.A.: Faserstofftabellen, Textilglasfasem (Z.ges.Textilind. 69 (1967), pp.839-846):

filament (elementary fiber), a practically continuous fiber with defineddiameter of the single fiber

staple fiber, non continuous fiber with defined diameter of the singlefiber.

Linear products made of textile fibers include among others thefollowing:

sliver, consisting of a continuous assembly of slightly bonded staplefibers in a practically parallel arrangement (not or nearly not twistedstaple fibers). The sliver has a defined linear density and is thesource material of staple fiber yarns and plied yarns.

Textile fibers are processed to linear products such as, e.g., yarns andto areal products such as, e.g., fabrics or braidings; they can be usedtoo for reinforcement of a matrix, e.g., of synthetics for themanufacture of composites.

The so-called quartz glass fibers and filament yarns which haveestablished themselves on the market are manufactured by the rodspinning process formed from a quartz melt at temperatures greater than2000° C. Considerable technical resources are required, which means thatthe prices for the corresponding products are relatively high.

It is also possible to leach glass filament yarn and the textileproducts manufactured therefrom with acids (DE-OS 2 609 419, GP-PS 2094363). Leached silica products manufactured by this method are used up to1100° C. As, however, their mechanical properties are very weak, in thecase of textiles heavy fabrics around 600-1300 g/m² are mainly used. Ithas not been possible to establish a broad field of application intextile processing of the respective yarns because of these weakmechanical properties.

It has, however, been possible to manufacture silica fibers withexcellent properties by a new production method under advantageousconditions, (DE-PS 2 900 990 and DE-PS 2 900 991). A sodium silicatefilament yarn with a drawing off speed of at least 30 m/min (in anexample at least 350 m/min) is manufactured in a first processing stepfrom sodium silicate solutions by the dry spinning process. Thisproduct, which tends to hydrolyze, is transformed to silica fibers bytreatment with acid and/or salt solutions containing hydrogen ions at aretention time of 1 to 15 minutes.

DE-PS 2 900 991 does not give details as to the conditions under whichthe sodium silicate fibers are fed immediately from the dry spinningunit into the treatment bath: due to the different processing speeds andretention times this is not easily understandable from a technical pointof view. In the examples quoted in the DE-PS 2 900 991 also, referenceis made to the transformation of "yarn pieces of 1 m length" and Patentclaims 6 to 9 clearly refer to the product type "fiber" in the sense ofstaple fiber or fiber short cut. For chemico-physical reasons textileproducts made of quartz, leached silica and silica fibers can be used upto ca. 1100° C. The DE-PS 2 900 991 quoted does not however report onthis.

Since about 1943 textile glass silver has been manufactured in a onestage process by the drum drawing process (DE-PS 715 884, GB-PS 755 626,DE-AS 1 199 935, DE-AS 1 270 748). Glass is melted at 1250° to 1300° C.and drawn by a rotating drum from a bushing at a speed of V₁ up toapprox. 50 m/sec. The adjoining continuous glass filaments are scrapedoff the drum with the additional aid of a flow of air prior to completerotation on the drum. Over the width of the drum there is a cone-shapedcollecting channel; the sliver formed here is pulled out of the pointedend of the collecting channel and wound at a, compared to V₁, low speedof V₂ up to 10 m/sec: "drum drawing process". The linear density (tex)of the sliver can be adjusted among others by the ratio V₁ : V₂.

Prior to the drawing drum maximum 1% textile size is applied to thecontinuous glass filaments to give among other the textile glass sliveran appropriate drawing force through adhesion. The textile glass sliverproduced in this way consists of fibers with a staple length of approx.50-1000 mm. After twisting, glass staple fiber yarns with a lineardensity in the range of 125 text to 2000 tex are usually obtained.

Inexpensive textile products made from these glass staple fiber yarnsare used, as a substitute for asbestos, for example as sealings or asthermal insulation material at a continuous application temperature upto approx. 300° C. For chemico-physical reasons, products made fromglass staple fiber yarns are not suitable for applications above atemperature range of 400°-500° C.

Textile products made from ceramic fiber yarns are used at temperaturesabove 400°-500° C. (in some cases as a substitute for asbestos). Ceramicfiber yarns are made from, among other raw materials, ceramic fibers ofvarious lengths on well known production units (slivers manufactured oncarding machines, and yarns manufactured on ring spinning frames). Apartfrom technical limitations in processing and application, ceramicfibers, similar to asbestos fibers, are also suspected of causingcancer, due to the fact that their size--some fibers are less than 3 μmin diameter--permits them to enter the lungs easily (Hodgson, A. A.,"Alternatives to Asbestos, The Pros and Cons", Critical Reports onApplied Chemistry, Vol. 26, John Wiley & Sons, Chichester, N.Y., 1989).

U.S. Pat. No. 3,760,049 describes a process for continuouslymanufacturing high temperature resistant oxide filament yarns(continuous fibers, e.g., 3Al₂ O₃ : 1B₂ O₃ : 3SiO₂). Green fibersmanufactured by the dry spinning process (V₁ =40-60 m/min) aretransported relaxed as loops on a conveyor belt through the furnaces (V₂=approx. 0.4 m/rain).

Organic constituents, which enable the extrusion through spinnerettes,are removed by thermal decomposition at temperatures up to approx. 1200°C. and the crystalline structure, which determines the strength, isformed.

It is well known that this type of yarn can be used up to 1200° C. andabove. The high raw material and processing costs are responsible forthe high selling price. The application in high temperature technologyis therefore limited. Staple fiber yarns are not known.

Thus there is an urgent need for economical and health compatibleinorganic textile slivers and staple fiber yarns which can be processedto a wide range of textile products and which can be used attemperatures above 400°-500° C. while maintaining, at the same time,their good mechanical properties.

SUMMARY OF THE INVENTION

The object of the invention is a method for the production of textilesilica slivers with good mechanical properties, taking into account andsupplementing DE-PS 2 900 991 with regard to dry spun sodium silicatefilament yarn and its treatment in acid solutions and/or salt solutionscontaining hydrogen ions.

The invention involves the combination of the dry spinning of sodiumsilicate filament yarn followed by the continuous formation of sodiumsilicate sliver by the drum drawing process and direct transportationinto the post treatment line.

The sodium silicate filament yarn freshly extruded through thespinnerettes is drawn by the rotating drum after passing through thedrying chimney and being lubricated with textile size. In deciding onthe composition of the size, care should be taken that it is soluble inthe acid bath which follows so as not to hinder the reaction of thesodium silicate filaments. The aqueous solution (preparation) given inDE-PS 2 900 991 can be used as sizing agent.

The minimum spinning speed is 350 m/min. However, spinning speeds V₁ ofmore than 600 m/min and less than 1200 m/min have proved to beadvantageous. Too low and too high speeds cause malfunctions in thespinning process, which make industrial production inefficient.

It is furthermore important that retaining the sodium silicate filamentson the drum for a short period has proved advantageous. Thus,atmospheric moisture or carbon dioxide which, as is well known, reactphysically and chemically with sodium silicate, do not harm thefilaments.

Prior to complete rotation on the drum--as described above--thefilaments are scraped off, intermingled in a chamber and drawn offlaterally via a twisting head at a speed V₂ lower than the spinningspeed V₁. The linear density of the sodium silicate sliver can beinfluenced by the ratio of the yarn speeds V₁ : V₂.

In the case that the sodium silicate sliver enters the post treatmentline at a speed below 200 m/rain, there will be no malfunctions. Thisgives an advantageous ratio of the speeds V₁ : V₂ of between 5 and 10.The transportation of the sliver from the drawing drum into the posttreatment line can also be supported by an air injector.

It was unexpectedly found that the open character of the sodium silicatesliver has a positive effect on the speed of the chemical reaction inthe aqueous acid or salt solution containing hydrogen ions; theretention time could be reduced to less than one minute; 20-30 secs.were found to be sufficient. The short retention time has a beneficialeffect on the processing conditions, the plant size and, consequently onthe manufacturing costs.

The textile silica sliver formed in the hydrogen ion bearing acid orsalt solution is deposited in zigzags on conveyor belts and transportedthrough the individual zones of the post treatment line.

After the calcinating furnace, the sliver must be treated withapproximately 1% textile size to protect the fiber surface againstabrasion and to improve the adhesion of the filaments to one another inrespect to winding up on the bobbins and to textile processing. A 10%aqueous solution (preparation) of a surfactant salt of ammonia(G 3634 ofAtlas Chemie Co.). can be used as sizing agent.

The intermingling of the textile silica sliver in air jets is possiblein principle. It is recommended that this procedure be carried outgently to avoid breakage of the individual silica filaments and/orstaple fibers. Apart from the intermingling of the pure silica sliver,mixed yarns with interesting properties for the later application can bemanufactured: filaments or yarns with supplementary properties can beadded, for example before the air jet, and intermingled with the textilesilica sliver in the air jet.

Depending on the number of holes in the spinnerette, the throughput ofthe spinning solution to be extruded, the spinning speed and the ratioV₁ : V₂, a broad range of sliver linear densities can be manufactured.Customer wishes and accepted standards usually determine the lineardensity of the yarn. The most common ones are likely to be lineardensities of around 125 tex and 330 tex.

Textile silica slivers and silica staple fiber yarns made therefrom areprocessed to, e.g., yarns, cords, braidings and fabrics. These textileproducts are used among others for insulation and heat protectionpurposes at temperatures above 400°-500° C., particularly up to 1100° C.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing shows the main features of the process of theinvention.

DETAILED DESCRIPTION

The water content of the sodium silicate filaments coming from aspinnerette 1 is reduced to a value of approximately 15-30% by weight ina drying chimney 2 by air in a direct flow or rising in a counterflow.Thereafter textile size is applied, for example, by a kiss roll 3. Thenthe filament yarn is taken up by a drawing drum and scraped off prior tocomplete rotation on the drum 4, intermingled in a conical chamber anddrawn off laterally. By means of a transportation godet 5 and a zigzagtransporting device, possibly also supported by an injector nozzle 5a,the sodium silicate sliver formed is transported to the entrance of anacid bath (which is the entrance to the post-treatment line). Thetransformation takes place in the acid bath 6, after which the formedtextile silica sliver is washed at station 7. Thereafter the sliverfalls from an acid-resistant conveyor belt onto a heat-resistantconveyor belt and is transported through a drying zone 8 and calcinatingzone 9. The textile size is then applied at station 10 and dried atstation 11. Before winding onto the bobbins 13, the sliver can beintermingled in an air jet 12 and, if necessary, a yarn with additionalproperties can be added.

The invention is explained in more detail by the following examples,which should not be construed as limiting the scope of the invention. Inthe examples, the conditions in accordance with DE 2 900 991 with regardto the formation of the sodium silicate spinning solution the sodiumsilicate filame and the post-treatment conditions are taken intoaccount. The frictional properties of the single staple fibers areinfluenced by the stick-slip behavior of the textile silica sliver,which has an influence on further processing. The stick-slip behaviorcan be characterized by the maximum drawing force which is determined,with the help of a tensile testing machine, by recording in a diagramthe rate of elongation as a function of the load applied. The peak ofthe curve shown in the diagram represents the maximum drawing force.

EXAMPLE 1

Sodium silicate with a molecular ratio Na₂ O/SiO₂ =1/2.48 and aviscosity of 240 Pa.s (30° C.) is extruded to sodium silicate filamentyarn through two spinnerettes, each with 120 holes. The spinning speedwas set at 750 m/min by the drawing drum. A ratio V₁ : V₂ of 8 was setby the speed of the following godets so that the silver formed was fedzigzag to the post-treatment line at approximately 94 m/min. The speedof the conveyor belts which transport the sliver through the zones ofthe post-treatment line was 10 m/min. Drying was done at approximately150° C., calcinating was done at approximately 800° C.

The following data were measured on the sized textile silica sliver andon single fibers:

    ______________________________________                                        linear density of the sliver                                                                      275 tex                                                   breaking tenacity (single filament)                                                               37 cN/tex                                                 maximum drawing force (sliver)                                                                    5-6N                                                      breaking tenacity   approximately 11 cN/tex                                   (staple fiber yarn, twisted)                                                  ______________________________________                                    

EXAMPLE 2

Spinning conditions as in Example 1.

The sodium silicate sliver was formed at a ratio V₁ : V₂ of 4. At thehigh sodium silicate sliver speed of approximately 190 m/min., it wasnot possible to post treat and wind the textile silica sliver ontobobbins without faults occurring. The data summarized in the followingtable were determined on short lengths of yarn:

    ______________________________________                                        linear density of the sliver                                                                      approximately 134 tex                                     filament diameter   9.2 μm                                                 breaking tenacity (filament)                                                                      40 cN/tex                                                 maximum drawing force (sliver)                                                                    4-5N                                                      breaking tenacity   approximately 12 cN/tex                                   (staple fiber yarn, twisted)                                                  ______________________________________                                    

EXAMPLE 3

Sodium silicate filament yarn was drawn off from a spinnerette with 120holes at a speed of 1000 m/min. The sliver was formed at a ratio V₁ : V₂of 8. The following table shows the results of the textile silicasliver:

    ______________________________________                                        linear density of the sliver                                                                      135 tex                                                   filmament diameter  9.1 μm                                                 breaking tenacity (filament)                                                                      38 cN/tex                                                 maximum drawing force (sliver)                                                                    5-6N                                                      breaking tenacity   approximately 10 cN/tex                                   (staple fiber yarn, twisted)                                                  ______________________________________                                    

What is claimed is:
 1. A textile silica sliver consisting of silicastaple fibers 50-1000 mm long, the single fibers having a breakingtenacity of 20-50 cN/tex and the textile silica sliver having, at alinear density of 50-2000 tex according to type, a maximum drawing forceof 2 to 20N.
 2. A process for manufacturing textile silica slivers, inwhich a sodium silicate filament yarn is manufactured from amanufactured sodium silicate solution by a dry spinning process which,immediately downstream of a drying chimney, is drawn off by a rotatingdrawing drum with a speed V₁ of at least 350 m/min and is directlytransformed to a sodium silicate sliver at a ratio V₁ :V₂ greater than 1and this sodium silicate sliver is transported directly into an entranceof a downstream post-treatment line with a speed V₂ lower than speed V₁,and is continuously transformed in an acid bath into textile silicaslivers and is, as such, supplied with a standard textile size, woundonto bobbins.
 3. The process according to claim 2, wherein the spinningspeed V₁ is 600 to 1200 m/min.
 4. The process according to claim 2 or 3,wherein, upstream of said drawing drum the sodium silicate filament yarnis lubricated with textile size, easily soluble in the succeeding acidbath.
 5. The process according to claim 2 or 3, wherein the sodiumsilicate sliver is transported directly and continuously from saiddrawing drum while forming zigzags to said entrance of saidpost-treatment line at a speed V₂ of less than 200 m/min.
 6. The processaccording to claim 2 or 3, wherein the drawing ratio V₁ :V₂ is 5 to 10.7. The process according to claim 2 or 3, wherein the transport ofsodium silicate sliver from said drawing drum to said entrance of saidpost-treatment line is supported by one of a transport godet and a flowair from an air injector nozzle.
 8. The process according to claim 2 or3, wherein the textile sodium silicate sliver is transformedcontinuously into textile silica sliver in said acid bath of saidpost-treatment line and is then washed, dried and calcinated.
 9. Asilica staple fiber yarn manufactured from textile silica sliveraccording to claim
 1. 10. Twisted yarns, cords, braidings and fabricsmanufactured from textile silica sliver according to claim
 1. 11. Methodof use of twisted yarns, cords, braidings and fabrics according to claim10 at temperatures higher than 400° to 500°.